Electrochemical activation and capacitance enhancement of expanded mesocarbon microbeads for high-voltage, symmetric supercapacitors

To increase the specific energy of supercapacitors (SCs), the expanded mesocarbon microbead (EM-CMB) is electrochemically activated in 1 M tetraethylammonium tetrafluoroborate in propylene carbonate (TEABF(4)/PC) to construct a high-voltage but symmetric SC. The EMCMB is successfully made from MCMB through the oxidation in a solution containing concentrated H2SO4, HNO3 and KMnO4 followed by a thermo-expansion treatment at 800 degrees C. This carbon with a specific surface area of only 93.2 m(2) g(-1) shows excellent capacitive performance after the electrochemical activation process in the highly positive or very negative potential regions in 1 M TEABF(4)/PC, especially when an aqueous-based binder, KOHpartially-neutralized polyurethane-polyacrylic acid (denoted as PUPAH(6)K(4)) was employed. These electrochemically activated EMCMB-PUPAH(6)K(4) electrodes are able to be charged and discharged reversibly in a wide potential range between -2.6 V and 1.4 V (vs. Ag/AgNO3). Consequently, a 4V SC consisting of two identical EMCMB-coated electrodes, i.e., symmetric, with good capacitive performances in 1 M TEABF(4)/PC has been successfully demonstrated, showing the great application potential in the advanced high-voltage SCs. (C) 2020 Elsevier Ltd. All rights reserved.